Glossary of Terms: L

L_Mn, Lmin
Minimum Level. The lowest sampled level during the instrument’s run time allowing for the unit’s Response Time setting (Fast or Slow).
L_Mx, Lmax
Maximum Level. The highest sampled level during the instrument’s run time allowing for the unit’s Response Time setting (Fast or Slow).
Latent period
The time that passes between exposure to a harmful substance or agent and the first sign(s) of damage or illness. Also known as incubation period.
Lavg, LAV
Lavg is the average sound level measured over the run time. This becomes a bit confusing when thresholds are used. Any sound below the threshold is not included in this average. Remember that sound is measured in the logarithmic scale of decibels therefore the average cannot be computed by simply adding the levels and dividing by the number of samples. When averaging decibels, short durations of high levels can significantly contribute to the average level.
Lethal concentration that will kill 50 percent of the test animals within a specified time. See LD50.
Liquid Crystal Display.
The dose required to produce the death in 50 percent of the exposed species within a specified time.
LDN (Level day night)
Representing the Day/Night sound level, this measurement is a 24-hour average sound level where 10 dB is added to all of the readings that occur between 10pm and 7am. This is primarily used in community noise regulations where there is a 10 dB “penalty” for nighttime noise. Typically LDN’s are measured using A weighting, a 3 dB Exchange Rate, and no Threshold.
Light Emitting Diode.
LEL meters
Scale for measurement for flammable gases by open path infrared detectors.
Percentage of the Lower Explosive Limit (for example, 10% LEL of Methane is approx. 0.5% by volume).
Daily personal noise exposure level.
Leq, L_EQ (Equivalent Level)
The true equivalent sound level measured over the run time. The term LEQ is functionally the same as LAVG except that it is only used when the Exchange Rate is set to 3 dB and the threshold is set to none.
Level (LFT)
Notation used to represent sound pressure level measurements in IEC/ISO notation, where the measurements are made with particular frequency (F) and time (T) response parameters. For an actual measurement, the F and T parameters are replaced by standardized notation for those parameters.
Lower Flammable Limit.
A formless fluid that takes the shape of its container, but does not necessarily fill it.
Liter (L)
A measure of capacity - one quart equals 0.9L.
Ln, LnX (Exceedance Level)
Exceedance levels represent the percent of the run time that was spent at or above the corresponding dB level. Example
An L40 equal to 73dB would mean that for 40% of the run time, the decibel level was equal to or higher than 73dB.
Liquefied Natural Gas.
Restricted to one spot or area in the body and not spread throughout it. Compare with systemic.
A specific set of procedures for ensuring that a machine, once shut down for maintenance, repair or other reason, is secured against accidental start-up or movement of any of its parts for the length of the shutdown.
Measurements recorded by the dosimeter at regular intervals.
Long term exposure limit (LTEL).
The 8 hour LTEL is the time-weighted average concentration for a normal 8 hour day to which most workers may be repeatedly exposed, day after day, without adverse effect. Also known as TWA or time-weighted average.
Loss control
Measures taken to prevent and reduce loss. Loss may occur through injury and illness, property damage, poor work quality, etc.
Lower explosive limit (LEL)
The lower limit of flammability of a gas or vapor at ordinary ambient temperatures expressed in percent of the gas or vapor in air by volume. This limit is assumed constant for temperatures up to 120°C (250°F). Above this, it should be decreased by a factor of 0.7 because explosibility increases with higher temperatures.
Liquefied Petroleum Gas made up of Propane and Butane.
Lpk, L_Pk (Peak Level)
Peak is the highest instantaneous sound level that the microphone detects. Unlike the Max Level, the peak is detected independently of the unit’s Response Time setting (Fast or Slow). Example: The peak circuitry is very sensitive. Test this by simply blowing across the microphone.